Solar inverters are components that are commonly found in photovoltaic (PV) power systems. The purpose of a solar inverter is to transform direct current (DC) generated by a PV system into alternating current (AC), which can be sent into a power grid or consumed on site. These inverters can be used either in concert with battery systems or to directly power certain devices. They also tend to have a few identifying features that are specifically intended to be used with PV arrays, such as maximum power point tracking (MPPT). Some inverters that are used to tie a PV array into a power grid also have protection against the islanding phenomenon.
When photovoltaic panels are used to generate electricity from solar radiation, the resulting output is a variable direct current. This is similar to the type of electricity found in batteries, and it must be changed into alternating current before it can power a home or business. The process of altering DC into AC is performed by an inverter, though most of these devices are designed to work with non-variable direct current. Unlike most other inverters, a solar inverter is designed specifically to work with the variable DC generated by PV arrays.
MPPT is one of the specialized features that can be built into a solar inverter. This technology allows the solar inverter to apply a load to each PV cell in order to obtain the highest level of power possible. Several different algorithms can be used in MPPT systems, though they are all intended to increase efficiency in this general manner.
The two main types of solar inverters are defined by whether they are meant to be used in off-grid or grid-tied applications. Off-grid inverters are used to directly power a home or business that does not receive electricity from any outside source. Grid-tied units are required for applications where the home or business is connected to an external power grid. In addition to providing power to a local site and charging reserve batteries, grid-tied units are also capable of returning excess electricity into the system. Since the premises can receive power from either the grid or an onsite PV array, additional precautions may be necessary.
In most cases, grid-tied inverters are meant to shut off if the premises become disconnected from the external power grid. Certain circumstances can lead a solar inverter to continue functioning after such a disconnect, which is a phenomenon known as islanding. Many solar inverters contain anti-islanding measures to prevent this from occurring, and such features are sometimes required by local utilities before a PV array can be tied into the grid. Other inverters have circuitry that can intentionally cut the premises off from the grid so that the PV array will only provide electricity to the local site.